This invention relates to stable liquid suspensions of finely divided particulate matter and to a method useful for determining their capacity to emit hydrogen sulfide.
It is often preferred in the textile dyeing and finishing art to use products which are in the form of liquid compositions. Such compositions have certain advantages over powdered or granular compositions. They are dust-free and they are better suited for use in automated equipment wherein they are pumped in metered quantities from a storage or holding container to a textile treatment apparatus. It is usually desired that the successive charges be uniform. This is especially true with regard to dyeing, wherein it is important that each charge of a given liquid dye composition be of the same strength, so that consistent dyeings can be achieved over a given period of time during which several successive:charges will be delivered from a given container to a given dyeing apparatus. It is desirable, therefore, that the liquid remain pumpable and easily stirrable, so that uniformity can be restored, if necessary, when a charge is to be delivered from the container to the, textile treatment (e.g. dyeing) apparatus. It is also desirable that the liquid be sufficiently stable so that it will remain uniform throughout the period of its residence in a container.
In the field of sulfur dyes the switch from dry powders or granules to liquids for the dyeing of textile materials was made several years ago with the advent of prereduced sulfur dye liquids, i.e. aqueous solutions of sulfur dyes which are in the reduced (leuco) form. Such liquids are usually produced by heating a sulfur dye in an aqueous alkaline medium and invariably they involve the presence of one or more inorganic sulfides, such as sodium sulfide, and/or one or more inorganic polysulfides. Such a compound may be carried over from a thionation reaction by which a sulfur dye is produced, or it may be generated in situ during the solubilization of such a dye as a result of the action of alkali on unreacted sulfur from the thionation reaction which is present with the dye, or it may be added to the aqueous alkaline medium as a reducing agent during the solubilization of the dye or for the purpose of preventing premature reoxidation of the leuco dye during shipment or storage, or its presence may result from a combination of these factors. Because of the adverse effects of sulfides on the environment and especially because of the potential health risks associated with the possible generation of dangerous amounts of toxic hydrogen sulfide gas by intentional or accidental addition of acid to a dye liquid containing sulfides, a concerted effort has been made to produce prereduced sulfur dye liquids of decreased sulfide content. While progress has been made, the goal of a commercially acceptable prereduced sulfur dye liquid which is sulfide-free or of such low sulfide content as to be essentially risk-free but which has the stability and other properties required by the textile dyeing industry has heretofore not been achieved.
Aqueous suspensions of sulfur dyes in solid particulate form can be produced which are sulfide-free or of such low sulfide content as to pose little or no sulfide-related hazard to humans or their environment. However, such compositions which have all of the other properties necessary to make them viable alternatives to the prereduced sulfur dye liquids have heretofore not been available at an acceptable cost. The present invention provides such compositions as well as liquid suspensions of other materials which are in solid particulate form.